In a communication system, especially in a mobile communication system, when a user is inaccessible, for example, when the user is outside the service area, when the user equipment is turned off, when the user is busy or when the user has subscribed to a service of Do Not Disturb (DND), a call from other users cannot be put through, i.e. the call to the user is not finished. In this case, generally, the called user cannot know whether he is called by another user, because the called user cannot acquire the call information about the calling user. Thus, the called user may miss some important calls.
To solve the problem, in the case that there is a missing call to a called user, two service solutions for notifying the called user of the missing call are proposed in the prior art.
In one service solution, a called Home Location Register (HLR) in the existing network constructs a missing-call short message containing at least the calling number and the current time, and sends the constructed missing-call short message to the called home Short Message Center (SMC); the called home SMC sends the missing-call short message to the called user when the called user is accessible. Here, the called user being accessible means that the called user is in a normal operating state and thus may receive a short message sent by the home SMC.
In the above first service solution, all the HLRs in the existing network need to be upgraded to enable the HLRs to construct and send the missing-call short message containing at least the calling number and the current time upon detecting that there is a missing call. In the above first service solution, a called user needs to subscribe to the short message notification service for missing calls in the home HLR. When detecting a missing call, the called HLR first checks whether the called user has subscribed to a service of Call Forward Busy or a service of Call Forward No Answer; if the called user has subscribed to the service of Call Forward Busy or the service of Call Forward No Answer, the called HLR triggers the service of Call Forward Busy or the service of Call Forward No Answer and continues with the processing based on the procedure of the service of Call Forward Busy or the service of Call Forward No Answer. Otherwise, the called HLR checks whether the called user has subscribed to the short message notification service for missing calls; if the called user has subscribed to the short message notification service for missing calls, the called HLR constructs a missing-call short message and sends the constructed missing-call short message to the called home SMC, and the called home SMC sends the missing-call short message to the called user when the called user is accessible. The called HLR returns a forward rejection to the calling end office if the called user has not subscribed to the short message notification service for missing calls.
In another service solution, a voice mailbox is used to notify a called user of a missing call. When detecting a missing call, the called HLR triggers the forward service and forwards the call to the voice mailbox of the called user based on an ordinary procedure of the forward service, and the calling user may leave a message in the voice mailbox of the called user. Thus, the called user may acquire the message of the calling user by accessing the voice mailbox of the called user.
In the above second service solution, the called user needs to subscribe in the home HLR to the service of Call Forward Busy or the service of Call Forward No Answer and set the forward number as the number of the voice mailbox of the called user. Thus, when the calling user calls the called user and the call cannot be put through, the call may be forwarded by the called HLR to the mailbox of the called user based on the ordinary procedure of the forward service.
In the above first service solution, all the HLRs in the existing network need to be upgraded to enable the HLRs to construct and send a missing call short message. Therefore, it is of much significance to the existing network to implement the first service solution, and it is very difficult to implement the solution and the cost is very high, which is very unfavorable for the spreading and application of the notification services for missing calls.
In the above second service solution, the calling user needs to connect to the voice mailbox and leave a message therein, thus the called user cannot in time acquire enough information about the calling user if the calling user did not leave a message or the calling user did not leave the identification information thereof after connecting to the voice mailbox. In addition, for leaving a message, the calling user needs to connect to the voice mailbox of the called user and pay for the call; for acquiring the message, the called user needs to access the voice mailbox and pay for the call too. Therefore, with the second service solution, it is possible that the called user cannot in time acquire enough information about the calling user, and both the calling user and the called user pay for the call, which is also very unfavorable for the spreading and application of the notification services for missing calls.